The present invention relates to a displacement type scroll fluid machine and, more particularly, to a scroll fluid machine, a scroll member and a processing method thereof, in which a curve of each of a pair of volute bodies is formed by an algebraic spiral.
A conventional scroll fluid machine comprises a fixed scroll and an orbiting scroll respectively having volute bodies of the same configuration and eccentrically combined with each other. As a volute configuration, an involute curve is generally used in which a volute pitch and a thickness of a volute wall become constant. As an advantage using the involute curve as the volute curve, it can be mentioned that processing is easily executed in which inward and outward volute curves can simultaneously be processed by a simple cutter, because a normal pitch of the volute is constant. However, since the thickness of the volute wall is constant, stress of a central portion of the volute body, which becomes the highest pressure, is raised. Thus, this is apt to become a problem in relation to strength. That is, the thickness is decided from constraint on the strength. The winding number of the volute body is decided from a running pressure ratio that is a design condition. A height of the volute body, a volute pitch and the like are decided from a stroke volume or piston displacement. If a configuration of one of the volute bodies, for example, a orbiting scroll is decided, a configuration of a fixed scroll in mesh with the orbiting scroll is decided such that an inside or inward envelope of a orbiting inward curve is selected to a fixed inward curve. Further, since a central portion of the volute body is also high in inside pressure difference, the conventional scroll fluid machine is disadvantageous in that a reduction in performance is likely to occur due to internal leakage of fluid. Moreover, since the volute pitch is constant in the involute curve, a displacement changing ratio is also constant. Accordingly, in a case where a built-in volume ratio, that is, a ratio between a sealed displacement (stroke volume) at the outermost periphery and a sealed volume at the innermost periphery tends to increase within a predetermined dimension, a problem arises in that, if the winding number of the volute increases, the volute pitch is reduced, and, because the volute wall thickness is constant, an orbiting radius is reduced, and the stroke volume is also reduced.
In U.S. Pat. No. 3,802,809, the volute wall thickness of a portion adjacent to the central portion of each of the volute bodies is thickened or increases so as to be capable of withstanding high pressure. Furthermore, in U.S. Pat. No. 2,324,168 and Japanese Patent Laid-Open No. 3-11102, the volute pitch is changed to change the built-in volume ratio.
In U.S. Pat. No. 3,802,809, because the volute wall thickness of a winding beginning or start portion of each of the volute bodies increases or is thickened, the problem relating to stress is addressed. Since, however, a region in which the thickness of the volute wall increases is limited to a portion of the winding beginning or start, an advantage to reduce the internal leakage of the fluid through an end face of the volute body is reduced. Further, since the thickness of the volute wall is constant within a portion except for the winding start portion, it is impossible to increase both the stroke volume and the built-in volume ratio within a predetermined dimension similarly to the involute curve.
Moreover, in the scroll fluid machine disclosed in U.S. Pat. No. 2,324,168 and Japanese Patent Laid-Open No. 3-11102, a volute pitch is changed to change a built-in volume ratio. However, for example, when the volute pitch is reduced from the outer periphery of the volute to the center thereof in an attempt to increase the built-in volume ratio, the more a location approaches a central portion (winding start) of the volute, the less the thickness of the volute wall is reduced, and no consideration is given with respect to the strength. On the contrary, since the more a location approaches the outer periphery of the volute, the more the thickness of the volute wall increases. Accordingly, the stroke volume is reduced. In this manner, a vortex curve capable of reducing or miniaturizing the volute body less than the involute curve in a case where both the stroke volume and the built-in volume ratio increase and in a case of the same or identical stroke volume and built-in volume ratio is unknown. Furthermore, a geometrical theory of the volute body in which the volute pitch and the thickness of the volute wall change, that is, an arrangement or constructional method of the vortex curve and the volute body does not become clear or apparent.